Goals for air traffic controllers and/or aircraft pilots may include: a) to more efficiently utilize airspace; and b) to promote the provision of safe takeoffs/landings for aircraft under a wide range of weather conditions. Required Navigation Performance (RNP) is a concept aimed at meeting these goals. Previously, an airplane's track-keeping and navigational capabilities were defined relative to ground-based navigation aids, such as VOR (Very high frequency Omni-directional Range) or NDB (Non-Directional radio Beacon). However, with RNP, an airplane's navigational capability is defined in terms of the performance and integrity of its installed on-board equipment. Accordingly, a number of navigation solutions may currently be implemented, such as satellite navigation systems (exs—GNSS (Global Navigation Satellite Systems) and GPS (Global Positioning Systems)), DME/DME (Distance Measuring Equipment) and/or VOR/DME, for providing an airplane with a certain degree of navigational precision/navigational capability. The higher the degree of navigational capability/performance of an aircraft, the more precisely the aircraft may be able to follow a pre-determined ground track, thereby allowing for certain routes to be placed closer together and further allowing for more effective use of airspace. Also, improved navigational capability may allow for an approach to be precisely flown in the vicinity of terrain, resulting in lower approach minimums.
A related concept to RNP is Estimated Position Uncertainty (EPU), which is a value which may be calculated by an airplane's navigation system (ex—(FMS)-Flight Management System) to indicate the airplane's degree of position uncertainty due to such factors as the number of GPS satellites in view, or the accuracy of ground-based navigational aids (exs.—VOR, DME, etc.). An additional concept related to RNP is Flight Technical Error (FTE) which is the degree of precision with which an airplane may be flown (either manually or on autopilot) along a desired navigational track. Two types of routes that RNP-capable aircraft may utilize are: 1) RNAV (Area Navigation) routes and; 2) RNP routes.
RNAV routes require that an airplane's Total System Error (TSE), which is equal to the sum of EPU and FTE (i.e., TSE=EPU+FTE) is within 1* the RNAV value ninety-five percent (95%) of the time. For instance, with an RNAV 2 route (i.e., required RNAV performance is 2.0 Nautical Miles (NM)), if the position uncertainty (EPU) were 0.5 NM, a pilot would be allowed 1.5 NM of FTE to remain within the RNAV value (1* RNAV), the RNAV value being equal to 2.0 NM. Knowing the amount of FTE available to him/her in a given scenario may promote a pilot's ability to better maintain the required navigational track within the 1* RNAV boundaries. Further, if the pilot needed to deviate from a planned route for weather, an available indication as to just how far the pilot can deviate (i.e., the amount of FTE available), while staying within the 1×RNAV boundary would allow the pilot to make such deviation without having to make a specific request to ATC (Air Traffic Control), thereby promoting reduction of communication burdens for air traffic controllers/pilots.
RNP routes typically require that an airplane be within 1* RNP ninety-five percent (95%) of the time. Also, RNP routes typically have to provide monitoring and alerting to ensure that the probability of the aircraft exceeding 2* RNP is no greater than 10E-7. For example, with certain approaches, where the RNP value can be as low as 0.1 NM, this equates to only 607 feet to the 95% boundary (ex—the 1* RNP boundary) and 1214 feet to the alerting boundary (ex—the 2×RNP boundary).
A number of on-board navigation solutions, such as lateral and vertical deviation indicators (ex—CDIs (Course Deviation Indicators)) and navigation performance scales for indicating EPU and allowable FTE are currently available. These currently available solutions are aimed at making it easier for pilots to maintain an aircraft on course (ex—within the 1* RNP/RNAV boundaries). However, the drawbacks of the currently available solutions are: a) they fail to explicitly indicate the allowable FTE (ex—allowable deviation), often limiting FTE by artificially reducing permitted deviation and; b) they lack the ability to indicate/provide an accurate location of an airplane which has navigated beyond the 1* RNP/RNAV boundaries.
Thus, it would be desirable to provide a navigation solution which addresses the problems associated with current solutions.